Studies On The Immune Function Of Attenuated Duck Hemorrhagic Disease Virus Live Vaccine

A new infectious disease of ducks with conspicuous symptoms of darked feather follicleand with hemorrhages in organ and intestine occurred in Fujian, Zhejiang and Guangdongsince1990. The disease was named as Duck hemorrhagic disease (DHD). It was caused by anew type of herpesivrus different from duck Plague.Antibiosis various medicine,currently available vaccines and hyper immune serum(yolkantibody) have failed to prevent the disease, which led to much economic losses in duckindustry, especially in Muscovy duck industry. In order to understand the pathogen andpathogenesy of the disease, the aetiology, pathology and epidemiology were studied in ourlaboratory of the Institute of Animal Husbandry and Veterinary Medicine, Fujian Academy ofAgricultural Science at the present.But there was a few works in immunology. So, studies onimmune responses in Muscovy duck were done in the experimental investigation.The resultswere as follows:1Detection of relative weight of immunity organCompared with the control group, there was a significant decreased in the index of bursaat1-3days after immunization(P<0.05), but they were no significant difference in spleen andthymus at early immunization(p>0.05); and then there were higher than that of the controlgroup in the index of thymus after immunization at3-28d,which were significantly higherthan that of control group after5-21d (P<0.05), and changes of the index at7-14wereextremely remarkably(P<0.01). The index of spleen was significant differences at7-28d(P<0.05), especially at7day (P<0.01); and there were no significant difference in the index ofbursa, but higher than the control one.2Determination of humoral immune functionIgG antibodies was detected by Indirect ELISA.The result showed that the IgGantibodies can be detected after7d, and increased until to21d, then began to decreasesllowlly, but still higher than that of critical value.3Cellular immune function assayLymphocyte proliferation test were applied to detect the numerical result at OD490nmafter Peripheral blood mononuclear cells were incubated with phytohemagglutinin (PHA), the results of the experiment indicated that there were significant differences at7-21daysafter immunization (P<0.05), especially at7-10days.But the T-lymphoid cell value ofperipheral blood was decreased remarkably at1day after immunization(P<0.01). that was thesame as detection of index of immunity organ,which suggested that DHDV is capable oflowering down the immune function transitorily. And then have the ability to induce cellularimmune responses, effectively increases the ability of the body to fight against virus.4Measure of the relative value of IFN-α mRNATwo standard curve method was used to detect the level of IFN-α mRNA.The resultshowed that the mRNA levels increased to6.57times at1hour and peaked at9hour at19.26times.then maintained at a high level from6.57to19.26times at1to9hour, later it declined.All that showed that inmunomodulatory effects in the early stage of infection, the cytotoxic Tcells, macrophages and NK cells was induced to inhibit virus replication directly or indirectly,so that improved the humoral and cellular immunologic function of the duck, Whichcontribute to building immune protective effect for the early infection.So, DHDV Attenuated Vaccine can improve the resistant ability of Muscovy ducks toDHDV by increasing not only the humoral immune function, but also the cellular immunefunction.